Carbon fiber-reinforced composite (CFRC) materials are extensively used in the aerospace industry to enable significant weight savings due to their high in-plane specific strength and stiffness. However, this benefit is countered by their low out-of-plane properties, such as interlaminar strength, that make CFRC structures susceptible to delamination. To prevent delamination, through-the-thickness stitching has been shown experimentally alleviate the damage propagation due to impact in CFRCs. Material optimization of stitched composites is required to reduce delamination at a macroscale. Atomistic to macroscale structure-property relationships need to be established and quantified to reduce delamination behavior of stitched composites. This proposal presents a pathway to develop hierarchical multiscale modeling approach from all length scales to reduce delamination.

Carbon fiber-reinforced composite (CFRC) materials are extensively used in the aerospace industry to enable significant weight savings due to their high in-plane specific strength and stiffness. However, this benefit is countered by their low out-of-plane properties, such as interlaminar strength, that make CFRC structures susceptible to delamination. To prevent delamination, through-the-thickness stitching has been shown experimentally alleviate the damage propagation due to impact in CFRCs. Material optimization of stitched composites is required to reduce delamination at a macroscale. Atomistic to macroscale structure-property relationships need to be established and quantified to reduce delamination behavior of stitched composites. This proposal presents a pathway to develop hierarchical multiscale modeling approach from all length scales to reduce delamination.

Latest revision as of 15:37, 28 April 2017

Contents

Carbon fiber-reinforced composite (CFRC) materials are extensively used in the aerospace industry to enable significant weight savings due to their high in-plane specific strength and stiffness. However, this benefit is countered by their low out-of-plane properties, such as interlaminar strength, that make CFRC structures susceptible to delamination. To prevent delamination, through-the-thickness stitching has been shown experimentally alleviate the damage propagation due to impact in CFRCs. Material optimization of stitched composites is required to reduce delamination at a macroscale. Atomistic to macroscale structure-property relationships need to be established and quantified to reduce delamination behavior of stitched composites. This proposal presents a pathway to develop hierarchical multiscale modeling approach from all length scales to reduce delamination.

The multiscale modeling approach will be performed at all individual length scales for both
the epoxy and carbon fiber constituents. These length scales are the structural, macro, meso, micro,
atomistic, and electronic length scales. At the atomistic level, atomistic potientals are required to
study the molecular behavior of epoxy chains and carbon-fiber crystalline structure under
deformation. These atomistic potentials can be calculated from Density Functional Theory and the
Modified Embedded Atom Theory (MEAM). MEAM has been previously used to calculate
the interatomic potential for saturated hydrocarbons. However, MEAM theory has not yet
been extended for cross-linked epoxy polymers that are not hydrocarbons. Therefore, a part of this
research will be used to develop interatomic potentials using MEAM for highly cross-linked
epoxies.

Using the interatomic potentials from MEAM, molecular dynamic (MD) simulations will
be performed to understand polymer chain mobility and the crystalline structure of the carbon
fiber. The strain rate mechanisms at the atomistic level will be evaluated and upscaled to a
macroscale continuum model. Additionally, course-graining MD can be used to reach higher
length scales to study the void nucleation behavior that results from cavitation, crazing, and chain
scission at the atomistic level. Interaction studies of the carbon fiber will also need to be
performed to evaluate the interfacial shear strength and interfacial stiffness between the carbon
fiber and epoxy. Recent studies have shown that the interfacial stiffness can vary near the graphite
atoms with different surface chemical groups to promote adhesion.

Information regarding void nucleation can be incorporated into a micromechancs finite
element model (FEM) to investigate void and crack interaction. Void and crack propagation can
be studied due to their interaction in polymer stitched composites at a macroscale continuum level.
Surrogate optimization techniques such as design of experiments and ensemble weighted method
can be subsequently employed to minimize the delamination behavior at the structural scale.

Experimental research is needed to understand and statistically quantify significant length
scale behavior in order to include their effects at higher length scales. Therefore, a design of
experiments approach will be used to evaluate the effect of each length scale factors on the
subsequently higher length scales. For instance, Changwoon et al. reported that cross-link density
and chain mobility can affect macroscale properties of polymer thermosets. Different
levels of cross-linking and chain mobility will be evaluated to understand their significance at
higher a macrolength scale. This research will provide validation of the models being used are
appropriate with respect to experimental data.